func (d *Data) publishDownresCommit(v dvid.VersionID, mutID uint64) {
	evt := datastore.SyncEvent{Data: d.DataUUID(), Event: DownsizeCommitEvent}
	msg := datastore.SyncMessage{Event: DownsizeCommitEvent, Version: v, Delta: mutID}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		dvid.Criticalf("unable to notify subscribers of event %s: %v\n", evt, err)
	}
}

// MergeLabels handles merging of any number of labels throughout the various label data
// structures.  It assumes that the merges aren't cascading, e.g., there is no attempt
// to merge label 3 into 4 and also 4 into 5.  The caller should have flattened the merges.
// TODO: Provide some indication that subset of labels are under evolution, returning
//   an "unavailable" status or 203 for non-authoritative response.  This might not be
//   feasible for clustered DVID front-ends due to coordination issues.
//
// EVENTS
//
// labels.MergeStartEvent occurs at very start of merge and transmits labels.DeltaMergeStart struct.
//
// labels.MergeBlockEvent occurs for every block of a merged label and transmits labels.DeltaMerge struct.
//
// labels.MergeEndEvent occurs at end of merge and transmits labels.DeltaMergeEnd struct.
//
func (d *Data) MergeLabels(v dvid.VersionID, m labels.MergeOp) error {
	dvid.Infof("Merging data %q (labels %s) into label %d ...\n", d.DataName(), m.Merged, m.Target)

	// Mark these labels as dirty until done, and make sure we can actually initiate the merge.
	if err := labels.MergeStart(d.getMergeIV(v), m); err != nil {
		return err
	}
	d.StartUpdate()

	// Signal that we are starting a merge.
	evt := datastore.SyncEvent{d.DataUUID(), labels.MergeStartEvent}
	msg := datastore.SyncMessage{labels.MergeStartEvent, v, labels.DeltaMergeStart{m}}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		d.StopUpdate()
		return err
	}

	// Asynchronously perform merge and handle any concurrent requests using the cache map until
	// labelvol and labelblk are updated and consistent.
	go func() {
		d.asyncMergeLabels(v, m)

		// Remove dirty labels and updating flag when done.
		labels.MergeStop(d.getMergeIV(v), m)
		d.StopUpdate()
		dvid.Infof("Finished with merge of labels %s.\n", m)
	}()

	return nil
}

// TODO -- Clean up all the writing and simplify now that we have block-aligned writes.
// writeBlocks ingests blocks of voxel data asynchronously using batch writes.
func (d *Data) writeBlocks(v dvid.VersionID, b storage.TKeyValues, wg1, wg2 *sync.WaitGroup) error {
	batcher, err := d.GetKeyValueBatcher()
	if err != nil {
		return err
	}

	preCompress, postCompress := 0, 0

	ctx := datastore.NewVersionedCtx(d, v)
	evt := datastore.SyncEvent{d.DataUUID(), IngestBlockEvent}

	<-server.HandlerToken
	go func() {
		defer func() {
			wg1.Done()
			wg2.Done()
			dvid.Debugf("Wrote voxel blocks.  Before %s: %d bytes.  After: %d bytes\n", d.Compression(), preCompress, postCompress)
			server.HandlerToken <- 1
		}()

		mutID := d.NewMutationID()
		batch := batcher.NewBatch(ctx)
		for i, block := range b {
			serialization, err := dvid.SerializeData(block.V, d.Compression(), d.Checksum())
			preCompress += len(block.V)
			postCompress += len(serialization)
			if err != nil {
				dvid.Errorf("Unable to serialize block: %v\n", err)
				return
			}
			batch.Put(block.K, serialization)

			indexZYX, err := DecodeTKey(block.K)
			if err != nil {
				dvid.Errorf("Unable to recover index from block key: %v\n", block.K)
				return
			}
			msg := datastore.SyncMessage{IngestBlockEvent, v, Block{indexZYX, block.V, mutID}}
			if err := datastore.NotifySubscribers(evt, msg); err != nil {
				dvid.Errorf("Unable to notify subscribers of ChangeBlockEvent in %s\n", d.DataName())
				return
			}

			// Check if we should commit
			if i%KVWriteSize == KVWriteSize-1 {
				if err := batch.Commit(); err != nil {
					dvid.Errorf("Error on trying to write batch: %v\n", err)
					return
				}
				batch = batcher.NewBatch(ctx)
			}
		}
		if err := batch.Commit(); err != nil {
			dvid.Errorf("Error on trying to write batch: %v\n", err)
			return
		}
	}()
	return nil
}

func (d *Data) mergeLabels(batcher storage.KeyValueBatcher, v dvid.VersionID, op labels.MergeOp) error {
	d.Lock()
	defer d.Unlock()

	d.StartUpdate()
	ctx := datastore.NewVersionedCtx(d, v)
	batch := batcher.NewBatch(ctx)

	// Get the target label
	targetTk := NewLabelTKey(op.Target)
	targetElems, err := getElements(ctx, targetTk)
	if err != nil {
		return fmt.Errorf("get annotations for instance %q, target %d, in syncMerge: %v\n", d.DataName(), op.Target, err)
	}

	// Iterate through each merged label, read old elements, delete that k/v, then add it to the current target elements.
	var delta DeltaModifyElements
	elemsAdded := 0
	for label := range op.Merged {
		tk := NewLabelTKey(label)
		elems, err := getElements(ctx, tk)
		if err != nil {
			return fmt.Errorf("unable to get annotation elements for instance %q, label %d in syncMerge: %v\n", d.DataName(), label, err)
		}
		if elems == nil || len(elems) == 0 {
			continue
		}
		batch.Delete(tk)
		elemsAdded += len(elems)
		targetElems = append(targetElems, elems...)

		// for labelsz.  TODO, only do this computation if really subscribed.
		for _, elem := range elems {
			delta.Add = append(delta.Add, ElementPos{Label: op.Target, Kind: elem.Kind, Pos: elem.Pos})
			delta.Del = append(delta.Del, ElementPos{Label: label, Kind: elem.Kind, Pos: elem.Pos})
		}
	}
	if elemsAdded > 0 {
		val, err := json.Marshal(targetElems)
		if err != nil {
			return fmt.Errorf("couldn't serialize annotation elements in instance %q: %v\n", d.DataName(), err)
		}
		batch.Put(targetTk, val)
		if err := batch.Commit(); err != nil {
			return fmt.Errorf("unable to commit merge for instance %q: %v\n", d.DataName(), err)
		}
	}
	d.StopUpdate()

	// Notify any subscribers of label annotation changes.
	evt := datastore.SyncEvent{Data: d.DataUUID(), Event: ModifyElementsEvent}
	msg := datastore.SyncMessage{Event: ModifyElementsEvent, Version: ctx.VersionID(), Delta: delta}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		dvid.Criticalf("unable to notify subscribers of event %s: %v\n", evt, err)
	}
	return nil
}

func (d *Data) moveElementInLabels(ctx *datastore.VersionedCtx, batch storage.Batch, from, to dvid.Point3d, moved ElementNR) error {
	labelData := d.GetSyncedLabelblk()
	if labelData == nil {
		return nil // no label denormalization possible
	}
	oldLabel, err := labelData.GetLabelAtPoint(ctx.VersionID(), from)
	if err != nil {
		return err
	}
	newLabel, err := labelData.GetLabelAtPoint(ctx.VersionID(), to)
	if err != nil {
		return err
	}
	if oldLabel == newLabel {
		return nil
	}

	var delta DeltaModifyElements
	if oldLabel != 0 {
		tk := NewLabelTKey(oldLabel)
		elems, err := getElementsNR(ctx, tk)
		if err != nil {
			return fmt.Errorf("err getting elements for label %d: %v", oldLabel, err)
		}
		if _, changed := elems.delete(from); changed {
			if err := putBatchElements(batch, tk, elems); err != nil {
				return fmt.Errorf("err putting deleted label %d element: %v", oldLabel, err)
			}
			delta.Del = append(delta.Del, ElementPos{Label: oldLabel, Kind: moved.Kind, Pos: from})
		}
	}
	if newLabel != 0 {
		tk := NewLabelTKey(newLabel)
		elems, err := getElementsNR(ctx, tk)
		if err != nil {
			return fmt.Errorf("err getting elements for label %d: %v", newLabel, err)
		}
		elems.add(ElementsNR{moved})
		if err := putBatchElements(batch, tk, elems); err != nil {
			return err
		}
		delta.Add = append(delta.Add, ElementPos{Label: newLabel, Kind: moved.Kind, Pos: to})
	}

	// Notify any subscribers of label annotation changes.
	if len(delta.Del) != 0 || len(delta.Add) != 0 {
		evt := datastore.SyncEvent{Data: d.DataUUID(), Event: ModifyElementsEvent}
		msg := datastore.SyncMessage{Event: ModifyElementsEvent, Version: ctx.VersionID(), Delta: delta}
		if err := datastore.NotifySubscribers(evt, msg); err != nil {
			return err
		}
	}

	return nil
}

// Notify any downstream downres instance of block change.
func (d *Data) publishBlockChange(v dvid.VersionID, mutID uint64, block dvid.IZYXString, blockData []byte) {
	evt := datastore.SyncEvent{d.DataUUID(), DownsizeBlockEvent}
	delta := deltaBlock{
		mutID: mutID,
		block: block,
		data:  blockData,
	}
	msg := datastore.SyncMessage{DownsizeBlockEvent, v, delta}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		dvid.Criticalf("unable to notify subscribers of event %s: %v\n", evt, err)
	}
}

func (d *Data) deleteElementInLabel(ctx *datastore.VersionedCtx, batch storage.Batch, pt dvid.Point3d) error {
	labelData := d.GetSyncedLabelblk()
	if labelData == nil {
		return nil // no synced labels
	}
	label, err := labelData.GetLabelAtPoint(ctx.VersionID(), pt)
	if err != nil {
		return err
	}
	tk := NewLabelTKey(label)
	elems, err := getElementsNR(ctx, tk)
	if err != nil {
		return fmt.Errorf("err getting elements for label %d: %v\n", label, err)
	}

	// Note all elements to be deleted.
	var delta DeltaModifyElements
	var toDel []int
	for i, elem := range elems {
		if pt.Equals(elem.Pos) {
			delta.Del = append(delta.Del, ElementPos{Label: label, Kind: elem.Kind, Pos: elem.Pos})
			toDel = append(toDel, i)
		}
	}
	if len(toDel) == 0 {
		return nil
	}

	// Delete them from high index to low index due while reusing slice.
	for i := len(toDel) - 1; i >= 0; i-- {
		d := toDel[i]
		elems[d] = elems[len(elems)-1]
		elems[len(elems)-1] = ElementNR{}
		elems = elems[:len(elems)-1]
	}

	// Put the modified list of elements
	if err := putBatchElements(batch, tk, elems); err != nil {
		return err
	}

	// Notify any subscribers of label annotation changes.
	evt := datastore.SyncEvent{Data: d.DataUUID(), Event: ModifyElementsEvent}
	msg := datastore.SyncMessage{Event: ModifyElementsEvent, Version: ctx.VersionID(), Delta: delta}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		return err
	}
	return nil
}

func (d *Data) splitLabelsCoarse(batcher storage.KeyValueBatcher, v dvid.VersionID, op labels.DeltaSplit) error {
	d.Lock()
	defer d.Unlock()

	d.StartUpdate()
	defer d.StopUpdate()

	ctx := datastore.NewVersionedCtx(d, v)
	batch := batcher.NewBatch(ctx)

	// Get the elements for the old label.
	oldTk := NewLabelTKey(op.OldLabel)
	oldElems, err := getElements(ctx, oldTk)
	if err != nil {
		return fmt.Errorf("unable to get annotations for instance %q, label %d in syncSplit: %v\n", d.DataName(), op.OldLabel, err)
	}

	// Create a map to test each point.
	splitBlocks := make(map[dvid.IZYXString]struct{})
	for _, zyxStr := range op.SortedBlocks {
		splitBlocks[zyxStr] = struct{}{}
	}

	// Move any elements that are within the split blocks.
	var delta DeltaModifyElements
	toDel := make(map[int]struct{})
	toAdd := Elements{}
	blockSize := d.blockSize()
	for i, elem := range oldElems {
		zyxStr := elem.Pos.ToBlockIZYXString(blockSize)
		if _, found := splitBlocks[zyxStr]; found {
			toDel[i] = struct{}{}
			toAdd = append(toAdd, elem)

			// for downstream annotation syncs like labelsz.  TODO: only perform if subscribed.  Better: do ROI filtering here.
			delta.Del = append(delta.Del, ElementPos{Label: op.OldLabel, Kind: elem.Kind, Pos: elem.Pos})
			delta.Add = append(delta.Add, ElementPos{Label: op.NewLabel, Kind: elem.Kind, Pos: elem.Pos})
		}
	}
	if len(toDel) == 0 {
		return nil
	}

	// Store split elements into new label elements.
	newTk := NewLabelTKey(op.NewLabel)
	newElems, err := getElements(ctx, newTk)
	if err != nil {
		return fmt.Errorf("unable to get annotations for instance %q, label %d in syncSplit: %v\n", d.DataName(), op.NewLabel, err)
	}
	newElems.add(toAdd)
	val, err := json.Marshal(newElems)
	if err != nil {
		return fmt.Errorf("couldn't serialize annotation elements in instance %q: %v\n", d.DataName(), err)
	}
	batch.Put(newTk, val)

	// Delete any split from old label elements without removing the relationships.
	// This filters without allocating, using fact that a slice shares the same backing array and
	// capacity as the original, so storage is reused.
	filtered := oldElems[:0]
	for i, elem := range oldElems {
		if _, found := toDel[i]; !found {
			filtered = append(filtered, elem)
		}
	}

	// Delete or store k/v depending on what remains.
	if len(filtered) == 0 {
		batch.Delete(oldTk)
	} else {
		val, err := json.Marshal(filtered)
		if err != nil {
			return fmt.Errorf("couldn't serialize annotation elements in instance %q: %v\n", d.DataName(), err)
		}
		batch.Put(oldTk, val)
	}

	if err := batch.Commit(); err != nil {
		return fmt.Errorf("bad commit in annotations %q after split: %v\n", d.DataName(), err)
	}

	// Notify any subscribers of label annotation changes.
	evt := datastore.SyncEvent{Data: d.DataUUID(), Event: ModifyElementsEvent}
	msg := datastore.SyncMessage{Event: ModifyElementsEvent, Version: ctx.VersionID(), Delta: delta}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		dvid.Criticalf("unable to notify subscribers of event %s: %v\n", evt, err)
	}
	return nil
}

// If a block of labels is deleted, the associated synapse elements should be changed to zero label elements.
func (d *Data) deleteBlock(ctx *datastore.VersionedCtx, block labels.DeleteBlock, batcher storage.KeyValueBatcher) {
	// Get the synaptic elements for this block
	chunkPt := dvid.ChunkPoint3d(*block.Index)
	tk := NewBlockTKey(chunkPt)
	elems, err := getElements(ctx, tk)
	if err != nil {
		dvid.Errorf("err getting elements for block %s: %v\n", chunkPt, err)
		return
	}
	if len(elems) == 0 {
		return
	}
	blockSize := d.blockSize()
	batch := batcher.NewBatch(ctx)

	// Compute the strides (in bytes)
	bX := blockSize[0] * 8
	bY := blockSize[1] * bX

	// Iterate through all element positions, finding corresponding label and storing elements.
	toDel := LabelPoints{}
	for _, elem := range elems {
		pt := elem.Pos.Point3dInChunk(blockSize)
		i := pt[2]*bY + pt[1]*bX + pt[0]*8
		label := binary.LittleEndian.Uint64(block.Data[i : i+8])
		toDel.add(label, elem.Pos)
	}

	// Delete any non-zero label elements from their respective label k/v.
	var delta DeltaModifyElements
	for label, pts := range toDel {
		tk := NewLabelTKey(label)
		elems, err := getElements(ctx, tk)
		if err != nil {
			dvid.Errorf("err getting elements for label %d: %v\n", label, err)
			return
		}
		save := false
		for _, pt := range pts {
			deleted, changed := elems.delete(pt)
			if changed {
				save = true
				delta.Del = append(delta.Del, ElementPos{Label: label, Kind: deleted.Kind, Pos: pt})
			}
		}
		if save {
			if len(elems) == 0 {
				batch.Delete(tk)
			} else {
				val, err := json.Marshal(elems)
				if err != nil {
					dvid.Errorf("couldn't serialize annotation elements in instance %q: %v\n", d.DataName(), err)
					return
				}
				batch.Put(tk, val)
			}
		}
	}

	if err := batch.Commit(); err != nil {
		dvid.Criticalf("bad commit in annotations %q after delete block: %v\n", d.DataName(), err)
		return
	}

	// Notify any subscribers of label annotation changes.
	evt := datastore.SyncEvent{Data: d.DataUUID(), Event: ModifyElementsEvent}
	msg := datastore.SyncMessage{Event: ModifyElementsEvent, Version: ctx.VersionID(), Delta: delta}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		dvid.Criticalf("unable to notify subscribers of event %s: %v\n", evt, err)
	}
}

// PutBlocks stores blocks of data in a span along X
func (d *Data) PutBlocks(v dvid.VersionID, mutID uint64, start dvid.ChunkPoint3d, span int, data io.ReadCloser, mutate bool) error {
	batcher, err := d.GetKeyValueBatcher()
	if err != nil {
		return err
	}

	ctx := datastore.NewVersionedCtx(d, v)
	batch := batcher.NewBatch(ctx)

	// Read blocks from the stream until we can output a batch put.
	const BatchSize = 1000
	var readBlocks int
	numBlockBytes := d.BlockSize().Prod()
	chunkPt := start
	buf := make([]byte, numBlockBytes)
	for {
		// Read a block's worth of data
		readBytes := int64(0)
		for {
			n, err := data.Read(buf[readBytes:])
			readBytes += int64(n)
			if readBytes == numBlockBytes {
				break
			}
			if err == io.EOF {
				return fmt.Errorf("Block data ceased before all block data read")
			}
			if err != nil {
				return fmt.Errorf("Error reading blocks: %v\n", err)
			}
		}

		if readBytes != numBlockBytes {
			return fmt.Errorf("Expected %d bytes in block read, got %d instead!  Aborting.", numBlockBytes, readBytes)
		}

		serialization, err := dvid.SerializeData(buf, d.Compression(), d.Checksum())
		if err != nil {
			return err
		}
		zyx := dvid.IndexZYX(chunkPt)
		tk := NewTKey(&zyx)

		// If we are mutating, get the previous block of data.
		var oldBlock []byte
		if mutate {
			oldBlock, err = d.loadOldBlock(v, tk)
			if err != nil {
				return fmt.Errorf("Unable to load previous block in %q, key %v: %v\n", d.DataName(), tk, err)
			}
		}

		// Write the new block
		batch.Put(tk, serialization)

		// Notify any subscribers that you've changed block.
		var event string
		var delta interface{}
		if mutate {
			event = MutateBlockEvent
			delta = MutatedBlock{&zyx, oldBlock, buf, mutID}
		} else {
			event = IngestBlockEvent
			delta = Block{&zyx, buf, mutID}
		}
		evt := datastore.SyncEvent{d.DataUUID(), event}
		msg := datastore.SyncMessage{event, v, delta}
		if err := datastore.NotifySubscribers(evt, msg); err != nil {
			return err
		}

		// Advance to next block
		chunkPt[0]++
		readBlocks++
		finish := (readBlocks == span)
		if finish || readBlocks%BatchSize == 0 {
			if err := batch.Commit(); err != nil {
				return fmt.Errorf("Error on batch commit, block %d: %v\n", readBlocks, err)
			}
			batch = batcher.NewBatch(ctx)
		}
		if finish {
			break
		}
	}
	return nil
}

// SplitLabels splits a portion of a label's voxels into a given split label or, if the given split
// label is 0, a new label, which is returned.  The input is a binary sparse volume and should
// preferably be the smaller portion of a labeled region.  In other words, the caller should chose
// to submit for relabeling the smaller portion of any split.  It is assumed that the given split
// voxels are within the fromLabel set of voxels and will generate unspecified behavior if this is
// not the case.
//
// EVENTS
//
// labels.SplitStartEvent occurs at very start of split and transmits labels.DeltaSplitStart struct.
//
// labels.SplitBlockEvent occurs for every block of a split label and transmits labels.DeltaSplit struct.
//
// labels.SplitEndEvent occurs at end of split and transmits labels.DeltaSplitEnd struct.
//
func (d *Data) SplitLabels(v dvid.VersionID, fromLabel, splitLabel uint64, r io.ReadCloser) (toLabel uint64, err error) {
	store, err := d.GetOrderedKeyValueDB()
	if err != nil {
		err = fmt.Errorf("Data type labelvol had error initializing store: %v\n", err)
		return
	}
	batcher, ok := store.(storage.KeyValueBatcher)
	if !ok {
		err = fmt.Errorf("Data type labelvol requires batch-enabled store, which %q is not\n", store)
		return
	}

	// Create a new label id for this version that will persist to store
	if splitLabel != 0 {
		toLabel = splitLabel
		dvid.Debugf("Splitting subset of label %d into given label %d ...\n", fromLabel, splitLabel)
	} else {
		toLabel, err = d.NewLabel(v)
		if err != nil {
			return
		}
		dvid.Debugf("Splitting subset of label %d into new label %d ...\n", fromLabel, toLabel)
	}

	evt := datastore.SyncEvent{d.DataUUID(), labels.SplitStartEvent}
	splitOpStart := labels.DeltaSplitStart{fromLabel, toLabel}
	splitOpEnd := labels.DeltaSplitEnd{fromLabel, toLabel}

	// Make sure we can split given current merges in progress
	if err := labels.SplitStart(d.getMergeIV(v), splitOpStart); err != nil {
		return toLabel, err
	}
	defer labels.SplitStop(d.getMergeIV(v), splitOpEnd)

	// Signal that we are starting a split.
	msg := datastore.SyncMessage{labels.SplitStartEvent, v, splitOpStart}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		return 0, err
	}

	// Read the sparse volume from reader.
	var split dvid.RLEs
	split, err = dvid.ReadRLEs(r)
	if err != nil {
		return
	}
	toLabelSize, _ := split.Stats()

	// Partition the split spans into blocks.
	var splitmap dvid.BlockRLEs
	splitmap, err = split.Partition(d.BlockSize)
	if err != nil {
		return
	}

	// Get a sorted list of blocks that cover split.
	splitblks := splitmap.SortedKeys()

	// Iterate through the split blocks, read the original block.  If the RLEs
	// are identical, just delete the original.  If not, modify the original.
	// TODO: Modifications should be transactional since it's GET-PUT, therefore use
	// hash on block coord to direct it to blockLabel, splitLabel-specific goroutine; we serialize
	// requests to handle concurrency.
	ctx := datastore.NewVersionedCtx(d, v)
	batch := batcher.NewBatch(ctx)

	for _, splitblk := range splitblks {

		// Get original block
		tk := NewTKey(fromLabel, splitblk)
		val, err := store.Get(ctx, tk)
		if err != nil {
			return toLabel, err
		}

		if val == nil {
			return toLabel, fmt.Errorf("Split RLEs at block %s are not part of original label %d", splitblk, fromLabel)
		}
		var rles dvid.RLEs
		if err := rles.UnmarshalBinary(val); err != nil {
			return toLabel, fmt.Errorf("Unable to unmarshal RLE for original labels in block %s", splitblk)
		}

		// Compare and process based on modifications required.
		remain, err := rles.Split(splitmap[splitblk])
//.........这里部分代码省略.........

func (d *Data) putChunk(chunk *storage.Chunk) {
	defer func() {
		// After processing a chunk, return the token.
		server.HandlerToken <- 1

		// Notify the requestor that this chunk is done.
		if chunk.Wg != nil {
			chunk.Wg.Done()
		}
	}()

	op, ok := chunk.Op.(*putOperation)
	if !ok {
		log.Fatalf("Illegal operation passed to ProcessChunk() for data %s\n", d.DataName())
	}

	// Make sure our received chunk is valid.
	if chunk == nil {
		dvid.Errorf("Received nil chunk in ProcessChunk.  Ignoring chunk.\n")
		return
	}
	if chunk.K == nil {
		dvid.Errorf("Received nil chunk key in ProcessChunk.  Ignoring chunk.\n")
		return
	}

	// Initialize the block buffer using the chunk of data.  For voxels, this chunk of
	// data needs to be uncompressed and deserialized.
	var blockData []byte
	var err error
	if chunk.V == nil {
		blockData = d.BackgroundBlock()
	} else {
		blockData, _, err = dvid.DeserializeData(chunk.V, true)
		if err != nil {
			dvid.Errorf("Unable to deserialize block in '%s': %v\n", d.DataName(), err)
			return
		}
	}

	// Perform the operation.
	block := &storage.TKeyValue{K: chunk.K, V: blockData}
	if err = op.voxels.WriteBlock(block, d.BlockSize()); err != nil {
		dvid.Errorf("Unable to WriteBlock() in %q: %v\n", d.DataName(), err)
		return
	}
	serialization, err := dvid.SerializeData(blockData, d.Compression(), d.Checksum())
	if err != nil {
		dvid.Errorf("Unable to serialize block in %q: %v\n", d.DataName(), err)
		return
	}

	store, err := storage.BigDataStore()
	if err != nil {
		dvid.Errorf("Data type imageblk had error initializing store: %v\n", err)
		return
	}
	ctx := datastore.NewVersionedCtx(d, op.version)
	if err := store.Put(ctx, chunk.K, serialization); err != nil {
		dvid.Errorf("Unable to PUT voxel data for key %v: %v\n", chunk.K, err)
		return
	}

	// Notify any subscribers that you've changed block.
	evt := datastore.SyncEvent{d.DataName(), ChangeBlockEvent}
	msg := datastore.SyncMessage{op.version, Block{&op.indexZYX, block.V}}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		dvid.Errorf("Unable to notify subscribers of ChangeBlockEvent in %s\n", d.DataName())
	}
}

// PutBlocks stores blocks of data in a span along X
func (d *Data) PutBlocks(v dvid.VersionID, start dvid.ChunkPoint3d, span int, data io.ReadCloser) error {
	store, err := storage.BigDataStore()
	if err != nil {
		return fmt.Errorf("Data type imageblk had error initializing store: %v\n", err)
	}
	batcher, ok := store.(storage.KeyValueBatcher)
	if !ok {
		return fmt.Errorf("Data type imageblk requires batch-enabled store, which %q is not\n", store)
	}

	ctx := datastore.NewVersionedCtx(d, v)
	batch := batcher.NewBatch(ctx)

	// Read blocks from the stream until we can output a batch put.
	const BatchSize = 1000
	var readBlocks int
	numBlockBytes := d.BlockSize().Prod()
	chunkPt := start
	buf := make([]byte, numBlockBytes)
	for {
		// Read a block's worth of data
		readBytes := int64(0)
		for {
			n, err := data.Read(buf[readBytes:])
			readBytes += int64(n)
			if readBytes == numBlockBytes {
				break
			}
			if err == io.EOF {
				return fmt.Errorf("Block data ceased before all block data read")
			}
			if err != nil {
				return fmt.Errorf("Error reading blocks: %v\n", err)
			}
		}

		if readBytes != numBlockBytes {
			return fmt.Errorf("Expected %d bytes in block read, got %d instead!  Aborting.", numBlockBytes, readBytes)
		}

		serialization, err := dvid.SerializeData(buf, d.Compression(), d.Checksum())
		if err != nil {
			return err
		}
		zyx := dvid.IndexZYX(chunkPt)
		batch.Put(NewTKey(&zyx), serialization)

		// Notify any subscribers that you've changed block.
		evt := datastore.SyncEvent{d.DataName(), ChangeBlockEvent}
		msg := datastore.SyncMessage{v, Block{&zyx, buf}}
		if err := datastore.NotifySubscribers(evt, msg); err != nil {
			return err
		}

		// Advance to next block
		chunkPt[0]++
		readBlocks++
		finish := (readBlocks == span)
		if finish || readBlocks%BatchSize == 0 {
			if err := batch.Commit(); err != nil {
				return fmt.Errorf("Error on batch commit, block %d: %v\n", readBlocks, err)
			}
			batch = batcher.NewBatch(ctx)
		}
		if finish {
			break
		}
	}
	return nil
}

func (d *Data) putChunk(chunk *storage.Chunk, putbuffer storage.RequestBuffer) {
	defer func() {
		// After processing a chunk, return the token.
		server.HandlerToken <- 1

		// Notify the requestor that this chunk is done.
		if chunk.Wg != nil {
			chunk.Wg.Done()
		}
	}()

	op, ok := chunk.Op.(*putOperation)
	if !ok {
		log.Fatalf("Illegal operation passed to ProcessChunk() for data %s\n", d.DataName())
	}

	// Make sure our received chunk is valid.
	if chunk == nil {
		dvid.Errorf("Received nil chunk in ProcessChunk.  Ignoring chunk.\n")
		return
	}
	if chunk.K == nil {
		dvid.Errorf("Received nil chunk key in ProcessChunk.  Ignoring chunk.\n")
		return
	}

	// Initialize the block buffer using the chunk of data.  For voxels, this chunk of
	// data needs to be uncompressed and deserialized.
	var blockData []byte
	var err error
	if chunk.V == nil {
		blockData = d.BackgroundBlock()
	} else {
		blockData, _, err = dvid.DeserializeData(chunk.V, true)
		if err != nil {
			dvid.Errorf("Unable to deserialize block in %q: %v\n", d.DataName(), err)
			return
		}
	}

	// If we are mutating, get the previous block of data.
	var oldBlock []byte
	if op.mutate {
		oldBlock, err = d.loadOldBlock(op.version, chunk.K)
		if err != nil {
			dvid.Errorf("Unable to load previous block in %q, key %v: %v\n", d.DataName(), chunk.K, err)
			return
		}
	}

	// Perform the operation.
	block := &storage.TKeyValue{K: chunk.K, V: blockData}
	if err = op.voxels.WriteBlock(block, d.BlockSize()); err != nil {
		dvid.Errorf("Unable to WriteBlock() in %q: %v\n", d.DataName(), err)
		return
	}
	serialization, err := dvid.SerializeData(blockData, d.Compression(), d.Checksum())
	if err != nil {
		dvid.Errorf("Unable to serialize block in %q: %v\n", d.DataName(), err)
		return
	}

	store, err := d.GetOrderedKeyValueDB()
	if err != nil {
		dvid.Errorf("Data type imageblk had error initializing store: %v\n", err)
		return
	}

	ready := make(chan error, 1)
	callback := func() {
		// Notify any subscribers that you've changed block.
		resperr := <-ready
		if resperr != nil {
			dvid.Errorf("Unable to PUT voxel data for key %v: %v\n", chunk.K, resperr)
			return
		}
		var event string
		var delta interface{}
		if op.mutate {
			event = MutateBlockEvent
			delta = MutatedBlock{&op.indexZYX, oldBlock, block.V, op.mutID}
		} else {
			event = IngestBlockEvent
			delta = Block{&op.indexZYX, block.V, op.mutID}
		}
		evt := datastore.SyncEvent{d.DataUUID(), event}
		msg := datastore.SyncMessage{event, op.version, delta}
		if err := datastore.NotifySubscribers(evt, msg); err != nil {
			dvid.Errorf("Unable to notify subscribers of event %s in %s\n", event, d.DataName())
		}
	}

	// put data -- use buffer if available
	ctx := datastore.NewVersionedCtx(d, op.version)
	if putbuffer != nil {
		go callback()
		putbuffer.PutCallback(ctx, chunk.K, serialization, ready)
	} else {
		if err := store.Put(ctx, chunk.K, serialization); err != nil {
			dvid.Errorf("Unable to PUT voxel data for key %v: %v\n", chunk.K, err)
//.........这里部分代码省略.........

func (d *Data) splitLabelsFine(batcher storage.KeyValueBatcher, v dvid.VersionID, op labels.DeltaSplit) error {
	d.Lock()
	defer d.Unlock()

	d.StartUpdate()
	defer d.StopUpdate()

	ctx := datastore.NewVersionedCtx(d, v)
	batch := batcher.NewBatch(ctx)

	var delta DeltaModifyElements
	toAdd := Elements{}
	toDel := make(map[string]struct{})

	// Iterate through each split block, get the elements, and then modify the previous and new label k/v.
	for izyx, rles := range op.Split {
		// Get the elements for this block.
		blockPt, err := izyx.ToChunkPoint3d()
		if err != nil {
			return err
		}
		tk := NewBlockTKey(blockPt)
		elems, err := getElements(ctx, tk)
		if err != nil {
			dvid.Errorf("getting annotations for block %s on split of %d from %d: %v\n", blockPt, op.NewLabel, op.OldLabel, err)
			continue
		}

		// For any element within the split RLEs, add to the delete and addition lists.
		for _, elem := range elems {
			for _, rle := range rles {
				if rle.Within(elem.Pos) {
					toAdd = append(toAdd, elem)
					toDel[elem.Pos.String()] = struct{}{}

					// for downstream annotation syncs like labelsz.  TODO: only perform if subscribed.  Better: do ROI filtering here.
					delta.Del = append(delta.Del, ElementPos{Label: op.OldLabel, Kind: elem.Kind, Pos: elem.Pos})
					delta.Add = append(delta.Add, ElementPos{Label: op.NewLabel, Kind: elem.Kind, Pos: elem.Pos})
					break
				}
			}
		}
	}

	// Modify the old label k/v
	if len(toDel) != 0 {
		tk := NewLabelTKey(op.OldLabel)
		elems, err := getElements(ctx, tk)
		if err != nil {
			dvid.Errorf("unable to get annotations for instance %q, old label %d in syncSplit: %v\n", d.DataName(), op.OldLabel, err)
		} else {
			filtered := elems[:0]
			for _, elem := range elems {
				if _, found := toDel[elem.Pos.String()]; !found {
					filtered = append(filtered, elem)
				}
			}
			if len(filtered) == 0 {
				batch.Delete(tk)
			} else {
				val, err := json.Marshal(filtered)
				if err != nil {
					dvid.Errorf("couldn't serialize annotation elements in instance %q: %v\n", d.DataName(), err)
				} else {
					batch.Put(tk, val)
				}
			}
		}
	}

	// Modify the new label k/v
	if len(toAdd) != 0 {
		tk := NewLabelTKey(op.NewLabel)
		elems, err := getElements(ctx, tk)
		if err != nil {
			dvid.Errorf("unable to get annotations for instance %q, label %d in syncSplit: %v\n", d.DataName(), op.NewLabel, err)
		} else {
			elems.add(toAdd)
			val, err := json.Marshal(elems)
			if err != nil {
				dvid.Errorf("couldn't serialize annotation elements in instance %q: %v\n", d.DataName(), err)
			} else {
				batch.Put(tk, val)
			}
		}
	}

	if err := batch.Commit(); err != nil {
		return fmt.Errorf("bad commit in annotations %q after split: %v\n", d.DataName(), err)
	}

	// Notify any subscribers of label annotation changes.
	evt := datastore.SyncEvent{Data: d.DataUUID(), Event: ModifyElementsEvent}
	msg := datastore.SyncMessage{Event: ModifyElementsEvent, Version: ctx.VersionID(), Delta: delta}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		dvid.Criticalf("unable to notify subscribers of event %s: %v\n", evt, err)
	}
	return nil
}

// TODO -- Clean up all the writing and simplify now that we have block-aligned writes.
// writeBlocks persists blocks of voxel data asynchronously using batch writes.
func (d *Data) writeBlocks(v dvid.VersionID, b storage.TKeyValues, wg1, wg2 *sync.WaitGroup) error {
	store, err := storage.BigDataStore()
	if err != nil {
		return fmt.Errorf("Data type imageblk had error initializing store: %v\n", err)
	}
	batcher, ok := store.(storage.KeyValueBatcher)
	if !ok {
		return fmt.Errorf("Data type imageblk requires batch-enabled store, which %q is not\n", store)
	}

	preCompress, postCompress := 0, 0

	ctx := datastore.NewVersionedCtx(d, v)
	evt := datastore.SyncEvent{d.DataName(), ChangeBlockEvent}

	<-server.HandlerToken
	go func() {
		defer func() {
			wg1.Done()
			wg2.Done()
			dvid.Debugf("Wrote voxel blocks.  Before %s: %d bytes.  After: %d bytes\n", d.Compression(), preCompress, postCompress)
			server.HandlerToken <- 1
		}()

		batch := batcher.NewBatch(ctx)
		for i, block := range b {
			serialization, err := dvid.SerializeData(block.V, d.Compression(), d.Checksum())
			preCompress += len(block.V)
			postCompress += len(serialization)
			if err != nil {
				dvid.Errorf("Unable to serialize block: %v\n", err)
				return
			}
			batch.Put(block.K, serialization)

			indexZYX, err := DecodeTKey(block.K)
			if err != nil {
				dvid.Errorf("Unable to recover index from block key: %v\n", block.K)
				return
			}
			msg := datastore.SyncMessage{v, Block{indexZYX, block.V}}
			if err := datastore.NotifySubscribers(evt, msg); err != nil {
				dvid.Errorf("Unable to notify subscribers of ChangeBlockEvent in %s\n", d.DataName())
				return
			}

			// Check if we should commit
			if i%KVWriteSize == KVWriteSize-1 {
				if err := batch.Commit(); err != nil {
					dvid.Errorf("Error on trying to write batch: %v\n", err)
					return
				}
				batch = batcher.NewBatch(ctx)
			}
		}
		if err := batch.Commit(); err != nil {
			dvid.Errorf("Error on trying to write batch: %v\n", err)
			return
		}
	}()
	return nil
}

func (d *Data) DeleteBlocks(ctx *datastore.VersionedCtx, start dvid.ChunkPoint3d, span int) error {
	store, err := storage.MutableStore()
	if err != nil {
		return fmt.Errorf("Data type labelblk had error initializing store: %v\n", err)
	}
	batcher, ok := store.(storage.KeyValueBatcher)
	if !ok {
		return fmt.Errorf("Data type labelblk requires batch-enabled store, which %q is not\n", store)
	}

	indexBeg := dvid.IndexZYX(start)
	end := start
	end[0] += int32(span - 1)
	indexEnd := dvid.IndexZYX(end)
	begTKey := NewTKey(&indexBeg)
	endTKey := NewTKey(&indexEnd)

	iv := dvid.InstanceVersion{d.DataName(), ctx.VersionID()}
	mapping := labels.MergeCache.LabelMap(iv)

	kvs, err := store.GetRange(ctx, begTKey, endTKey)
	if err != nil {
		return err
	}

	batch := batcher.NewBatch(ctx)
	uncompress := true
	for _, kv := range kvs {
		izyx, err := DecodeTKey(kv.K)
		if err != nil {
			return err
		}

		// Delete the labelblk (really tombstones it)
		batch.Delete(kv.K)

		// Send data to delete associated labelvol for labels in this block
		block, _, err := dvid.DeserializeData(kv.V, uncompress)
		if err != nil {
			return fmt.Errorf("Unable to deserialize block, %s (%v): %v", ctx, kv.K, err)
		}
		if mapping != nil {
			n := len(block) / 8
			for i := 0; i < n; i++ {
				orig := binary.LittleEndian.Uint64(block[i*8 : i*8+8])
				mapped, found := mapping.FinalLabel(orig)
				if !found {
					mapped = orig
				}
				binary.LittleEndian.PutUint64(block[i*8:i*8+8], mapped)
			}
		}

		// Notify any subscribers that we've deleted this block.
		evt := datastore.SyncEvent{d.DataName(), labels.DeleteBlockEvent}
		msg := datastore.SyncMessage{ctx.VersionID(), labels.DeleteBlock{izyx, block}}
		if err := datastore.NotifySubscribers(evt, msg); err != nil {
			return err
		}

	}
	return batch.Commit()
}

// stores synaptic elements arranged by label, replacing any
// elements at same position.
func (d *Data) storeLabelElements(ctx *datastore.VersionedCtx, batch storage.Batch, be blockElements) error {
	labelData := d.GetSyncedLabelblk()
	if labelData == nil {
		dvid.Infof("No synced labels for annotation %q, skipping label-aware denormalization.\n", d.DataName())
		return nil // no synced labels
	}

	// Compute the strides (in bytes)
	blockSize := d.blockSize()
	bX := blockSize[0] * 8
	bY := blockSize[1] * bX
	blockBytes := int(blockSize[0] * blockSize[1] * blockSize[2] * 8)

	toAdd := LabelElements{}
	for izyxStr, elems := range be {
		blockCoord, err := izyxStr.ToChunkPoint3d()
		if err != nil {
			return err
		}

		// Get the labels for this block
		labels, err := labelData.GetLabelBlock(ctx.VersionID(), blockCoord)
		if err != nil {
			return err
		}
		if len(labels) == 0 {
			continue
		}
		if len(labels) != blockBytes {
			return fmt.Errorf("Expected %d bytes in %q label block, got %d instead.  Aborting.", blockBytes, d.DataName(), len(labels))
		}

		// Group annotations by label
		for _, elem := range elems {
			pt := elem.Pos.Point3dInChunk(blockSize)
			i := pt[2]*bY + pt[1]*bX + pt[0]*8
			label := binary.LittleEndian.Uint64(labels[i : i+8])
			if label != 0 {
				toAdd.add(label, elem.ElementNR)
			}
		}
	}

	// Store all the added annotations to the appropriate labels.
	var delta DeltaModifyElements
	for label, additions := range toAdd {
		tk := NewLabelTKey(label)
		elems, err := getElementsNR(ctx, tk)
		if err != nil {
			return fmt.Errorf("err getting elements for label %d: %v\n", label, err)
		}

		// Check if these annotations already exist.
		emap := make(map[string]int)
		for i, elem := range elems {
			emap[elem.Pos.MapKey()] = i
		}
		for _, elem := range additions {
			i, found := emap[elem.Pos.MapKey()]
			if !found {
				elems = append(elems, elem)
				delta.Add = append(delta.Add, ElementPos{Label: label, Kind: elem.Kind, Pos: elem.Pos})
			} else {
				elems[i] = elem // replace properties if same position
			}
		}
		if err := putBatchElements(batch, tk, elems); err != nil {
			return fmt.Errorf("couldn't serialize label %d annotations in instance %q: %v\n", label, d.DataName(), err)
		}
	}

	// Notify any subscribers of label annotation changes.
	evt := datastore.SyncEvent{Data: d.DataUUID(), Event: ModifyElementsEvent}
	msg := datastore.SyncMessage{Event: ModifyElementsEvent, Version: ctx.VersionID(), Delta: delta}
	if err := datastore.NotifySubscribers(evt, msg); err != nil {
		return err
	}

	return nil
}